Modern integrated circuit IC devices typically employ shallow trench isolation and multi-level interconnects to meet the demands for increased functionality and faster processing speeds. However, planarization of interlevel dielectrics, conductive layers and trench dielectrics are required when using these technologies to obtain optimum fabrication results.
One technique that provides planarization and has received widespread acceptance in the semiconductor processing industry is chemical-mechanical polishing CMP.
CMP is used to planarize and remove surface topography irregularities of a material layer through chemical reaction and mechanical abrasion.
Typically a CMP process involves placing a substrate (e.g. a semiconductive wafer) face down on a polishing pad where the polishing pad is attached to a rotatable table, or platen. The polishing of the substrate by the polishing pad is normally performed with rotational, linear or orbital motion. Abrasive dispersions and chemical additives, known as slurry, are introduced onto the surface of the polishing pad while the polishing pad is being rotated and the substrate is pressed against the polishing surface of the polishing surface of the polishing pad. Additionally, the substrate may also be rotated in conjunction with the moving polishing pad.
The polishing of the substrate by the chemical-mechanical process is provided by chemical interaction of the slurry, which includes chemical reagents, with the substrate and abrasives contained within the slurry, where typical abrasives used in the CMP include silica, alumina and ceria. However, other abrasives may be used.
The polishing process starts with the chemical interaction between the slurry and the substrate (i.e. material layer) with the abrasives in the slurry, coupled with the movement of the polishing pad relative to the substrate, removing the reacted surface material from the substrate. The polishing process continues until the desired amount of the material layer is removed. Upon completion of the polishing process the substrate is subjected to a cleaning process to remove residual slurry and foreign particles.
However, by semiconductor fabrication standards CMP is inherently a dirty process, which in addition to a significant amount of foreign particles being introduced to the substrate surface also results in a significant amount of foreign particles, for example abrasive particles and by products of the planarization, being introduced to the polishing pad that can result in an undesirable built up of particles on the polishing pad, which is an effect known as ‘pad glazing’.
Pad glazing results in the smoothing of the upper surface (i.e. working surface) of the polishing pad causing a reduction in the abrasive properties of the polishing pad and consequently a reduction in the polishing rate.
Additionally, the ‘glaze’ is often unevenly distributed over a polishing pad surface, which can result in localized differences in polishing rate and increased polishing non-uniformity. Further, the foreign particles attached to the polishing pad can result in increased wafer defectivity such as scratches and particle residues.
One way to alleviate this problem has been via the use of deionised water being dispensed on the polishing pad to aid in the washing off of the foreign particles, however this technique is largely ineffective.
Another solution that has been adopted to address this problem is the use of a conditioning diamond disk that is used to remove the ‘glaze’ and other unwanted particles from the polishing pad.
The technique of conditioning the polishing pad with a conditioning device involves mechanically abrading the polishing pad surface to remove the glaze and ‘renew’ the polishing pad surface.
However, it has been found that the conditioning of a polishing pad with a conditioning disk typically results in the foreign particles being transferred to the conditioning disk and as a result a film builds up on the conditioning device and the conditioning capabilities of the conditioning disk are reduced resulting in a lower removal rate of unwanted particles from the polishing pad by the conditioning device and less uniform conditioning of the polishing pad by the conditioning device.
It is desirable to improve this situation.